Correct Pattern kept for Reference.-When a jig plate has been prepared and satisfactorily finished, it may then be used with care, as a guide through which the holes in other pieces can be drilled, tapped, or reamed, as the case may be. When one piece of work has been FIG. 82. edges of all the tools are considerably not come in contact with the hardened FIG 83. made, and the location of the holes is satisfactory in every respect, such a piece is best kept for purposes of reference. Drill Shanks all made alike to Gauge. -The best way to use a drilling jig is to have all the drill shanks, reamer shanks, and cutter-bar shanks, made exactly alike in dimensions. Bushes fit One Gauge. -In this case the bushings are accurately ground to fit one standard gauge, whatever sizes the holes to be drilled may be. Tool Edges preserved. -By adopting the above arrangement the cutting preserved, because they do walls of the holes of the bushings, as is obviously the case when the bushes are bored to the same diameter as the finished holes in the work. Steady Bearing.- A further important advantage is, that when at work the drills and reamers are kept perfectly steady, owing to the good fitting contact between the enlarged portion on the drill shank and the bushes. Lubrication and Cleanliness. This perfect slid ing contact is preserved by the careful use of a lubricant, and by keeping the parts quite clean. Uniformity in Product.-We have seen a number of machines working on this system with most excellent results. The holes drilled and reamed were alike to of an inch; each article was pierced with 1 1000 a number of different-sized holes, each hole serving as a bearing for an axle or a shaft, the latter being finally fixed in place without adjustment ever being necessary. Where the above system is not practised, there are various-sized bushes used on the same jig plate, i.e. each bush is ground to one standard diameter; but bars, reamers, and drills, of different diameters have their own respective bushes. It will therefore be clear that a considerable number of different-sized bushes are necessary, and since they have to be frequently removed and others substituted, there is a risk of fracture and an increase of wear. The length of these bushes is about one and a half diameter of the hole; and the space between the under side of the bush and the top side of the work is made as little as is practicable. In this way the steadiness of the tools when cutting is ensured. When holes have to be made at set angles to other holes or surfaces, there are two methods of doing the FIG. 84. work. Either the jig plate swings, or the drill spindle. In the former case there is generally a stop, against which the swing jig is turned to; while in the latter case the swing head of the drilling machine is turned over to the correct angle, as indicated by the marking which is shown in degrees on the rim of the turning joint. Right-hand and left-hand brackets, when used to support the opposite ends of spindles or shafts, may be drilled and reamed, while clamped between two jig plates. Each plate carries a separate set of bushes, and after the work has been machined on one side, the jig is simply reversed with the underside turned uppermost. Thus two plates may be held in one jig without removal while they are drilled, reamed, milled, and profiled respectively. CHAPTER V. TURRET LATHES. TURRET lathes are now made in all sizes, from the smallest, operating on minute watch screws and studs, to the largest, now suitable for the work in a general engineering workshop. A representative type of machine for doing lathe work, particularly that class coming between in. and 2 in. diameter, and less than 24 in. long, is here given in detail: The Hartness Flat Turret Lathe, made by The Jones and Lamson Machine Co. (Fig. 86). This lathe differs from other turret lathes principally in the form of its tool carriage and its tools; the turret is a flat circular plate, mounted on a low carriage, containing controlling mechanism. An important feature lies in the manner the turret is connected to the carriage, and the carriage to the bed; for unless these are perfectly rigid, they will not afford perfect control of the cutting tools. By referring to Fig. 87 it will be seen, in this enlarged view of the turret, that the base on which the various holders are secured is of large diameter. This is one of the distinct features of the machine. This base is scraped and padded to its seating on the carriage, and is secured by an annular gib. In a similar manner the carriage is fitted to the vee's of the bed, but in this case the gibs pass under the outside edge of the bed, the breadth of this bridge from V to V being sufficient to form an unyielding support to the tools. A further advantage is obtained by having the turret flat, since the indexing mechanism can be located with the index pin directly under the working tool so close as to permit no loss of motion between the tool and the locking pin. Hartness Flat Turret Lathe.-The turret is turned automatically to each position the instant the tool clears the work on its backward travel, and it is so arranged that, by raising and lowering the trip screws near the centre of the turret, it may be turned to three, four, or five of the six places without making any other stop. The power feed for the carriage is actuated by a worm shaft, the worm being held into the wheel by a latch which is disengaged by the feed stops. There are six feed stops, each being independent and adjustable. These stops are notched, flat bars placed side by side on the top of the bed. The lever in Fig. 88 actuates the tool slide. |